Reclamation of low-melting-point salts from black liquor



' Patented July 8, 1924..

JOSEPH E. PLUMSTEAD, OF WILMINGTON, -DELAWARE, ASSIGNOR TO THE JESSUP 2MOORE PAPER COL, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OFMASSACHUSETTS.

REGLAMATION OF LOW-MELTING-POINT SALTS FROM BLACK LIQUOR.

No Drawing.

To all whom it may concern:

Be it known that I, JosnrH E. PLUM- STEAD, a citizen of the UnitedStates, and resident of Wilmington, in the count of New Castle and Stateof Delaware, ave invented certain newand. useful Improve-- ments in theReclamation of Low-Melting- Point Salts from Black Liquor, of which thefollowing is a specification.

This invention relates to an improvement in the reclamation of valuescontained in that waste substance of the paper pulp industry commonlyknown as black liquor.

The principal object of the invention is the carrying out of a processby which the black liquor is evaporated to dryness in a manner whichwill prevent fusion of the" low melting point salts contained therein.

This invention contemplates the treatment of black liquor, whetherproduced by the so-called soda, sulphate or sulphite rocesses, or anyother process which pro uces a similar substance which might containsalts of a low melting point, such as those of the soda sulphur type andwherein it is desired to incinerate or otherwise evaporate to drynessand char the material containing these values.

The usual practice in the reclamation of such values is to pass theblack liquor slowly into a rotary incinerator of one type or another,which is supplied with heat from a grate fired furnace located at oneend. In this way the material being treated is progressively heated asit advances from the cold to the hot end of the incinerator. However, itis the universal experience of those practicing this reclamationprocess, where the black liquor contains salts of the the cold to thehot end of the incinerator. process is complicated by the fact thatthese soda sulphur salts have a lower melting point than carbonate ofsoda which exists in large quantities in this liquor. Tn using a gratefired incinerator, the hottest part of the fire is at the very front ofthe rotary furnace where the ash is hottest. Consequently there isfusion at the dis charge end. As a result the sodium sulphur salts inmelted condition adhere to the brick work of the furnace and form agummy fluid-like mass which has a tendency to cover up any particles ofblack ash not yet completely charred. In addition to this Applicationfiled December 15, 1923. Serial No. 681,008.

difliculty, when this mass is placed in the dissolving tanks, theefficiency of the solvent is decreased because of the physicalcharacteristic of this fused mass. It is, therefore, a problem toproperly incinerate and char the black liquor containing salts of a lowmelting point without reaching the points of fusion and volatilization.

I have discovered that in using dried carbon as pulverized fuel, ratherthan using grate fired coal, I can increase the capacity of the furnace,push the ash through faster, and complete the charring of the blackliquor without fusion. The results in a savmg of time, and preventsvolatilization of any values in the black ash through fusion, andeliminates the difiiculty in the dissolvmg step.

The pulverized dried carbon may be produced in any desired manner, but Ihave found it expedient to utilize that material usually produced as aworthless by-product 1n the dissolving step in the treatment of theblack ash, such as is described in my Patent No. 1,442,494.

Any desired combustion apparatus may be used which is adapted to burnpulverized or powdered fuel, it being only necessary that the flameproduced within the rotary incinerator be such that the incinerator isheated to its highest temperature within the incinerator and at a pointbetween the entry of the liquid black liquor and the point in theincinerator where the charred ash is produced. in this way theincineration of the black liquor is stopped at the black ash and is notcarried beyond to the point of fusion.

By practicing this method it will be readily seen that the black liquorbefore it reaches the point of ash, may be exposed to a heat greaterthan that which would produce fusion of the black ash. This conditionobtains by reason of the fact that when the black liquor is exposed tothe maximum heat it is in a fluid or semifiuid state, and by the timethe ash has been produced, the hottest part of the furnace has beenpassed and this ash is exposed to a decreasing degree of heat.

While I have specifically mentioned the utilization of dried carbon asfuel, as this material is most convenient for use among that class ofpaper pulp plants practicing the soda process, yet it will be evidentthat any kind of pulverized fuel will be satisfactory. The importantpoint of the process is that the hottest part of the incinerator shallbe reached by the material being treated therein before said materialreaches the discharge end of the incinerator. This is only possible whenpulverized fuel is used, as the flame produced thereby may be insertedinto the incinerator to any desired extent. I contemplate the use ofpulverized coal, coal dust, pulverized wood waste, and the like, eitheras substitutes for, or in combination With, the pulverized carbonmentioned above. 4

Having thus described my invention, what I claim is 1. A process ofrecovering values from black liquor which includes the steps of causingsaid liquor to pass through heat zones of varying intensity wherebyevaporation takes place and black ash is produced, said materialreaching the heat zone having the maximum temperature before evaporationis complete.

2. A process of recovering values from black liquor, which includes thesteps of passing said liquor through an increasing zone of heat and thenthrough a decreasing zone of heat.

3. A process of recovering values from black liquor containing sodiumsulphur salts, which includes the step of passing said material througha heat zone, the temperature of which is above the fusing point of saidsalts, before said liquor has reached a semi-fluid state, and thenthrough a heat. zone, the temperature of which is below the fusing pointof said salts.

4. A process of recovering inorganic values from black liquor whichincludes the step of passing said material through a heat zone, thetemperature of which is above the fusion point of the inorganic valuestherein, before said liquor has reached asemi-fluid state, and thenthrough a heat zone, the temperature of which is below the fusion pointof said values.

5. A process of recovering values from black liquor which includes thesteps of passing said liquor through a heat zone at a point inthe heattreatment previous to the formation of black ash, then passing saidmaterial through a heat zone, the temperature of which is below thefusion point of the values in the black ash, and continuing the heattreatment until substantially all the black liquor has been convertedinto black ash.

(i. A process for recovering sodium sulphur salts from black liquorwhich includes the steps of passing said liquor through a heat zone, thetemperature of which is above the melting point of said sodium sulphursalts, at a point in the heat treatment previous to the formation ofblack ash, and passing said material through a heat zone, thetemperature of which is below the melting point of said sodium sulphursalts after the formation of black ash.

7. A process of recovering sodium sulphur salts from black liquor whichincludes the steps of passing said liquor througl'i a. heat zone, thetemperature of which is, above the fusion point of black ash, previousto the formation of black ash, and then passing said material through aheat zone, the temperature of which is below the melting point of blackash, after the formation of black ash.

8. A process of recovering values from black liquor which includes thesteps of causing said liquor to pass through heat zones of difi'erentintensity, said material reaching the zone of maximum intensity beforeblack ash is produced.

9. A process of recovering sodium sulphur salts from black liquor whichincludes the steps of causing said liquor to pass through heat zones ofdifierent intensity, the zone of maximum intensity having a temperatureabove the melting point of said sodium sulphur salts, said liquorreaching said maximum heat zone before the production of substantialamounts of black ash.

In testimony whereof, I aflix my signature.

JOSEPH E. PLUMSTEAD.

